This research project involves the development of optical methods to quantify the total available oxygen content of epicardial tissue. Epicardial oxygen is found in three major pools - as oxygen dissolved in aqueous media, as oxygen bound to hemoblobin and as oxygen bound to myoglobin. In this proposal, instrumentation will be developed to simultaneously obtain reflectance spectra and phosphorescence from the same region of the epicardium and from this data determine P02 in cardiac circulation and obtain concentrations of the oxy and deoxy hemeproteins. Predictive ability of this reflectance method will be tested with hemoglobin/myoglobin mixtures in scattering media and in blood perfused rat hearts. After demonstration of feasibility in Phase I, Phase II will concentrate on developing the instrument for use in working perfused hearts and in NMR magnets to increase its utility for cardiac bioenergetic studies.The application of multivariate statistical techniques to analyze optical spectra opens up the prospect of monitoring multiple metabolic parameters simultaneously for use in evaluating cardiac ischemia and hypoxia. This instrument will quantify multiple aspects of tissue metabolism and oxygen supply/demand for research and clinical purposes.